Measuring and testing methods and apparatus employing x-rays



, June 19, 1951 F. FUA ErAL 2,557,868

MEASURING AND TESTING" METHOD AND APPARATUS EMPLOYING X-RAYS Filed March 12. 1948 4 Sheets-Sheet 1 FIG'J l 'l'.l.

INVENTORS June 19, 1951 F. FUA` r-:rAL 2,557,868

MEASURING 'AND TESTING METHOD AND APPARATUS EMPLOYING X-RAYS Filed March l2, 1948 4 Sheets-Sheet 2 ne. a

INVENTORS Frederic Na Faber-t c'. xfaaafs A BY ' A TORNEYS F. FUA T'AL MEASURING AND TESTING METHOD AND APPARATUS June 19;l 195.1

EMPLOYING X-RAYS T 4 Sheets-Sheet 3 Filed Marc-ri 12,1948

Flcs.y 5

'MULTIPLIER F G- n FLuoREscEN-r PHOTO TUBE SCREEN ASSEMBLY UNKNOWN A *PoyvER SUPPLY E? INVENEQRS FLuoREscENr sc REEN ASSEMBLY )M-ds MULTIPLIER M PHoTo TUBE ATTORNEYS A.C. AMPLIFIER June- 19, 1951 F. FUA ErAL 2,557,868

MEASURING AND TESTING METHOD AND APPARATUS n EMPLOYING X-RAYS Filed March 12, 1948 l 4 4 Sheets-Sheet 4 Haber- C. Meds' ORNE Y S Patented June 19, 1951 MEASURING 'ANDfIESTING"METHODSI`AND APPARATUS AEMPLOY'ING; X- RAY'S Frederic Flua New York, .Ni Y ,and- Robert C. Woods,- MontclainrN. .1.assignors to`.X-Ray EleetlfonicCorporation, NewYork, .N. .Y, acorporation of New York Application March- 12, 1948, SerialiNo.; 14,50f1

` 4,Claims. (Cl: 25m-83:3)

y This invention relates .to measuring 4and testing apparatus, and more particularly tomethods and a1: 1: aratu sV for examination of materials by X-'rays This application is a continuation-inpart of Fua and Woods Application, Serial No. 558,928, filed October 16, 1944, now Patent Ymoving fragile web, such as ametalffoil, withoutl a physical :contact therewith.

A prime purpose ofthe invention is Eto .provide an accurate andgreliable non-contact thickness .gage capa-bleef measuring variations in thickness toa vfraction of a per cent inv theiastmovi-ngproduct, hot or cold, of a` vmodern strip or rolling mill.r

Another feature relatesto an IX-ray ydeviceior ,testing the thickness Oimaterialssuch asgmetal foil webs, whereby greater sensitivity` intesting thickness or density .variations is attained.

A furtherfea-ture relates toan X-raytesting device for testing' variations in thickness or density across the width vof a moving ,metalweh such YfOr-example vas a continuously moving metal foil.

A stillvfurther feature relates to the novel organization, arrangement and relative location of parts which cooperate to produce a compact,

safe and reliable Xrayy testing device of the character to be described.

Other features and advantages not'specically enumerated will be apparent aftera consideration of the following-detailed description andthe appended claims.

vWhile-the inventionV will 'bedescribed' inconnection with the testing-of `metal foil andthe like, it will be understood-that 1in certain of its aspects, the invention is equally. well Vapplicable to the testing of a wide Vvariei',y-,of articles. described in detail below with theaid1of-the accompanying drawings, in which:

Fig. l is an end view of adeyice -for testing the edge of metal webs;

Fig. 21is aftop-planviewoi Fig. 1;

Fig. Bis an end view. of a. modification offFigS. l and 2; I

Fig.- 4.is.a,topplan view of Fig. 3;

Fig. 5 is afplan viewofaurther-,mOdied form of the Vdeviceillustrated :in Eig.- 1';

It .is

V from-the X-raytube 22 pass.

`electric cells I2, I3,

Fig. 6 is aside View oi y'the device illustratedin Fig.' 5;

Eig. '7 Vis a section, on an enlarged scale, on the Fig. Sis a partial bottom plan view of the testingY cell housing aperture Viewedin the direction of the arrows 8*-8 `in Fig. 7;

Fig. 9 isasection,onanenlarged scale, onthe line S-B--in Fig; 6;

Fig. lO'is asection, on ,an enlarged scale, on the line Ill- I0 vin-Fig. 6; and

Fig. 1l is afvdiagram schematically illustrating the functioning-ofthe invention. 1

Referring. to Figs.- 1.andf2, thereisshownan arrangement for testing the' thickness; 0r.: density of rcontinuously.v moving webs such as; metall'foil Webs. The vdevice compisesazmetal housing 1 l having arectangular-bore I8 eXtend-ingientirely through its length andqthrough which themetal web-;I/I.to-,betested is continuously fed. The housing I I also-has;a.cavity v20 invivhichv-is-placed a stand-ardvsample .lyof the metal foil of known thickness and density.- Communicating with the cavi-ty 2-0 is Ya. slit 2l vthrough vwhich .the X-rays Likewise a slit 2,3com-municates .with the bore .I 8 but adjacent voneside. onlyof .the bore so that the X-rays ini-p pinge only .on thelongitudinal edge. of ,the web I 4.

Mounted ,in .a .suitable cavity lbeneath ,the bore mand beneath the4 cavity. 'I Evare a pair-ofphoto- These cells are mounted so. that V,cell I2 lresponds only vto theX-rays which pass .through the edge of the web I4; while the cell I3 lresponds ,only to the Xfrays which pass ythroughthe stanlardfl. The cells I2,y I3, as

shown bythe multiplicitywof leads reaching them, are.4 preferably` ofthe multiplier type. Each .of the.- cells :I 2, I3 y may be connected vover conductors 2B,- 21 to a. respective `ampliiier 25Aand 25B.; as

lillustrated inl Fig. 1 to operate .a corresponding Nan-averag' geiifect over the entire-Width and changes: thickness ordensity might 3 give an improper indication of the actual thickness of the web.

Referring to Figs. 3 and 4, there is shown a device for measuring the density or thickness at any particular point or points across the width of the web while the latter is being fed continuously in the direction of its length. The device comprises a base 39 having a pair of parallel uprights 33 between which a pair of guide bars 31 extend. Adapted to slide along the bars 31 is a metal housing 30 containing on its interior an X-ray generator tube 3|, a light-sensitive or photo-electric cell 32 and a receptacle 35 containing a standard sample 36 of known thickness and density. It will be understood of course that suitable slits 4t, 4| are provided between the X-ray tube 3| and the photo-electric cell 32. The housing 30 also has a section 42 within which is enclosed another photo-electric cell 43 which is provided with a slit member 44 so that the X-rays from Vtube 3| also pass through said slit to the cell 43. The sections 42 and 45 of the housing 39 have a reentrant clear portion 45 and the metal foil or web 41 to be examined is supported on suitable guides (not shown) so as to be fed in a plane perpendicular to the X-ray beam 48. Whenit is desired to test only the edge section of the web 41, the entire unit is held in the position shown in Fig. 3. If, however, it is desired to examine any particular section of the width of the web 41 while the latter is being fed in the direction of the arrows, the entire unit 3G is moved towards the right, under control ofa suitable lever 49.

The effect of the foregoing arrangement is to provide, on the one hand, an electric current of undeviating peak or average magnitude proportional to the absolute density'or thickness value of a comparison standard sample and of an appropriate order to be directly compared, on the other hand, with the peak or average value of the output of a photocell which has been activated proportionately to the intensity of an X- ray beam penetrating an unknown sample. order to calibrate such apparatus for measuring by such comparison an unknown having any desired speciiication thickness or density, a sample of material having this specification characteristie is inserted in place of the unknown and the apparatus is then apprepriately adjusted so that the photocell output and the comparison current of undeviating magnitude are strictly comparable, for example, when they are connected in vvoltage opposition, so that the resultant voltage is zero. It will, of course, be understood that the gauge actually measures effective X- ray opacity along a predetermined path so that, if a sample being measured is of the specification density, then any departure from standard must be due to a change in its thickness, while, on the other hand, if a sample is of specification thickness, then any departure from standard must be due to a change in its density. For

example, the product of a rolling mill may be `vary in density due to internal ilaws.

In the modified form illustrated in Figs. 5-10,

inclusive, the apparatus is arranged to measure the thickness of the relatively narrow, moving, Sheet-metal strip 50 along its approximate cen- 4 ter line. The X-ray tube 5| is positioned horizontally in cabinet 52 beneath web 50. Its X-ray windows are in the target end 65 enclosed in chamber 53 from which, through aperture plates, one beam of X-ray passes upward through web '50 into upper photocell chamber 51 and another beam passes downward through a comparison standard held in place by the springs 66 into lower photocell chamber 61. The tube 5| receives its power supply, preferably A. C., through the shielded cable 59. It will be observed that the cabinet 52 in which the X-ray tube 5| and lower photocell 54 are enclosed and upon which Yarm 55 carrying upper photocell 56, being of -metal, aords ample electrostatic shielding for the parts it enclcses. The X-ray windows of the tube 5| are nevertheless encased in heavy- Walled chamber 53 for safety to restrict the outgoing X-ray to the apertures that guide the beams they form into the heavy-walled photocell chambers 51 and 61. The upper and lower photocells 56 and 54, of the multiplier type, are furnished with the necessary stepped-voltage power supply through the shielded cables 58 and 1|, respectively. The thickness of the walls of chambers 51, 53 and 61 must be sucient to prevent the escape of X-ray and to conne the beams to the desired paths. For this purpose, a

variety of materials sufce, e. g., brass, and afford needed electrostatic shielding as well. As disclosed in our copending application, Serial No. 688,896, iled August 7, 1946, now Patent 2,512,247, the accuracy and precision or the instrument is materially enhanced by selecting the thickness and material of the box walls to make them effective anti-magnetic shielding as well.

The upper photocell chamber 51 has an aperture 6B for the admission of X-ray. This aperture is cut through the massive wall of the chamber 51 proper and through a plate 6| which also serves as a retainer plate for a fluorescent screen assembly G8 which is preferably constructed according to the disclosures of our copending applications, Serial Nos. 658,903,` now abandoned, and 702,034, led April 2, 1946 and October 8, 1946, respectively. The assembly 6B is held rmly in place by springs 69 and comprises an outer aluminum foil layer, a middle layer 62 of iiuorescent material and an inner lead glass layer 64. The X-ray passing through aperture 60 penetrates foil layer 63, excites iiuorescent layer 62 and is stopped by lead glass layer 64. The aluminum increases the response of the fluorescent material to the X-ray and also reflects this response, in the form of light. The fluorescent light passes through the glass to excite upper photocell 56 proportionately to the intensity of the X-ray entering aperture {il} while the glass protects the photocell from deterioration and erratic excitation that would result from direct exposure to the X-ray.

The lower photocell chamber 61 isessentially the same as upper chamber 51 having a similar aperture 50 covered by a iiuorescent screen assembly 68 receiving X-ray from tube 5|. There is, however, arranged in the path of the X-ray entering lower chamber 61 a comparison standard holder slide 13 in which the springs 66 are arranged to position the holder properly. The

standard holder itself (not shown) is akin to a lantern slide holder, a frame of predetermined size and thickness conforming to the dimensions of slide 10 and interposing in the path of the X-ray reaching the screen 68 of lower chamber 61 only a piece of the metal web 50 being gaged known to be of true specification thickness. Lower photocell 54 is thus excited proportionately to the intensity of the X-ray penetrating the comparison standard. By suitable apparatus, the outputs of photocells 56 and 54 can be compared and a measure obtained of the thickness of the moving web 50.

One method of comparison, of course, is by visual comparison of separate output meters, as shown in Fig. l, but an improved method of comparison is shown schematically in Fig. l1, applied to the apparatus illustrated in Figs. 5-10, inclusive. The X-ray tube has an A. C'. power supply giving the X-ray emitted a pulsating characteristic. This pulsating X-ray penetrating the unknown above and the standard below is diminished by each proportionate to its individual absorption factor. Since the unknown and the sample are different only in thickness, if at all, the diierence in diminution of the X-ray will be a measure of their difference in thickness. The diminished beams now strike the upper and lower fluorescent screen assemblies, the light from which strikes the upper and lower photocells respectively. Since the amount of light is absolutely very small, it is preferable to use photocells of the well-known multiplier type. The output of the upper and lower cells will be two pulsating electric currents each a measure in amount, respectively, of the thickness of unknown and standard. These currents are bucked and their algebraic sum amplied to activate a meter which will indicate the amount and sign of the amplified signal and hence the amount and sign of the difference in thickness of unknown and standard.

The life and service reliability of the apparatus disclosed, especially its accuracy in commercial use, is lgreatly increased by operating all the electrical and electronic elements thereof well below their rated capacities. For example, the multiplier photocells are rated for a stepped voltage power supply to the anodes reaching 10100-1100 volts, but in this service operate best with a stepped power supply reaching 600 volt maximum.

While certain particular embodiments have been disclosed herein, it will be understood that various changes and modiications may be made therein without departing from the spirit and scope of the invention. It will be understood that the X-rays are chosen as to hardness or penetrating power so that very little, if any, can escape through the metal walls of the various housings and castings.

In the appended claims the expression crosssectional mass is used to define the quantity of X-ray absorbing material in the path of the X-ray beam. This is synonymous with geometrical thickness in a rolled metal sheet. It is also equivalent to the quantity of coating material per unit of area of a coated fabric.

The expression extended length of material is intended to include sheets, webs, rods, pipes 6 We claim:

1. The method of measuring the cross-sectional mass at different locations in an extended length of material which comprises directing, in one operation, a beam from a source of X-ray through a defined area of material of desired cross-sectional mass, intercepting said X-ray on a screen of fluorescent material having a light output proportional to X-radiation intercepted by it, directing the light generated by said screen upon a photo-cell having an output proportional to light directed upon it, measuring the output of said cell, directing, in a second operation, a substantially identical beam of X-ray through a like area of the extended length of material to be measured, intercepting said last-mentioned beam of X-ray on a screen of fluorescent material having a light output proportional to X-radiation intercepted by it, directing the light generated by said last-mentioned screen upon a photo-cell having an output proportional to light directed upon it, and measuring the output of the photocell in said second operation for comparison with the output of the photo-cell in said rst operation.

2. The method recited in claim 1 including the step of continuously moving said extended length of material across the path of the X-ray beam.

3. The method recited in claim 1 in which the X-ray directed through the dened area of material of desired cross-sectional mass and the X-ray directed through the like area of the extended length of material to be measured are simultaneously supplied from a single source of X-ray.

4. The method recited in claim 3 including the step of continuously moving said extended length of material across the path of the X-ray beam.

FREDERIC FUA. ROBERT C. WOODS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,094,318 Failla Sept. 28, 1937 2,097,760 Y Failla Nov. 2, 1937 2,189,623 Bourland Feb. 6, 1940 2,222,450 Trost Nov. 19, 1940 2,264,725 Shoupp et al. Dec. 2, 1941 2,301,251 Capen Nov. 10, 1942 2,349,429v Herzog May 23, 1944 2,370,163 Hare Feb. 27, 1945 2,401,288 Morgan et al. May 26, 1946 FOREIGN PATENTS Number Country Date 482,354 Great Britain June 19, 1936 OTHER REFERENCES Allen- Review of Scientific Instruments-Vol. 12, October 1941, pp. 484-488.

Smith-General Elec. Review-March 1, 1945, pp. 13-17. 

